RedundantStringConversion

SUGGESTION

Simplification

Summary

Avoid redundant string conversions when possible

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("RedundantStringConversion") to the enclosing element.

Disable this pattern completely by adding -Xep:RedundantStringConversion:OFF as compiler argument. Learn more.

Samples

Replacement

Shows the difference in example code before and after the bug pattern is applied.

 class A {
   private final Object o = new Object();
   private final String s = o.toString();
 
   void m() {
-    String v1 = s.toString();
-    String v2 = "foo".toString();
+    String v1 = s;
+    String v2 = "foo";
     String v3 = v2 + super.toString();
-    String v4 = 42 + String.valueOf((String) null);
-    String.format("%s", o.toString());
+    String v4 = 42 + (String) null;
+    String.format("%s", o);
   }
 }

Identification

Shows code lines which will (not) be flagged by this bug pattern.
A //BUG: Diagnostic contains: comment is placed above any violating line.

class A {
  private final Object o = new Object();
  private final String s = o.toString();

  String[] m() {
    return new String[] {
      o.toString(),
      // BUG: Diagnostic contains:
      s.toString(),
      String.valueOf(o),
      // BUG: Diagnostic contains:
      String.valueOf(s),
    };
  }
}

import java.math.BigInteger;
import java.util.Objects;

class A {
  private final BigInteger i = BigInteger.ZERO;

  void m1() {
    String s = i.toString();
    // BUG: Diagnostic contains:
    s += this.toString();
    s += super.toString();
    // BUG: Diagnostic contains:
    s += i.toString();
    s += i.toString(16);
    // BUG: Diagnostic contains:
    s += Objects.toString(i);
    // BUG: Diagnostic contains:
    s += Objects.toString(null);
    // BUG: Diagnostic contains:
    s += String.valueOf(i);
    // BUG: Diagnostic contains:
    s += String.valueOf(0);
    // BUG: Diagnostic contains:
    s += String.valueOf((String) null);
    s += String.valueOf(null);
    s += String.valueOf(new char[0]);
    s += String.valueOf(new char[0], 0, 0);
    // BUG: Diagnostic contains:
    s += Boolean.toString(false);
    // BUG: Diagnostic contains:
    s += Byte.toString((byte) 0);
    // BUG: Diagnostic contains:
    s += Character.toString((char) 0);
    // BUG: Diagnostic contains:
    s += Short.toString((short) 0);
    // BUG: Diagnostic contains:
    s += Integer.toString(0);
    // BUG: Diagnostic contains:
    s += Long.toString(0);
    // BUG: Diagnostic contains:
    s += Float.toString((float) 0.0);
    // BUG: Diagnostic contains:
    s += Double.toString(0.0);
  }

  void m2() {
    int i = 0;
    i += 1;
    i -= 1;
    i *= 1;
    i /= 1;
  }
}

import java.math.BigInteger;

class A {
  private final BigInteger i = BigInteger.ZERO;
  private final String s = i.toString();

  String[] m1() {
    return new String[] {
      // BUG: Diagnostic contains:
      s + this.toString(),
      s + super.toString(),
      // BUG: Diagnostic contains:
      s + i.toString(),
      s + i.toString(16),
      // BUG: Diagnostic contains:
      s + String.valueOf(i),
      // BUG: Diagnostic contains:
      s + String.valueOf(0),
      // BUG: Diagnostic contains:
      s + String.valueOf((String) null),
      s + String.valueOf(null),
      s + String.valueOf(new char[0]),
      s + String.valueOf(new char[0], 0, 0),
      //
      42 + this.toString(),
      42 + super.toString(),
      42 + i.toString(),
      42 + i.toString(16),
      42 + String.valueOf(i),
      // BUG: Diagnostic contains:
      42 + String.valueOf((String) null),
      42 + String.valueOf(null),
      42 + String.valueOf(new char[0]),
      42 + String.valueOf(new char[0], 0, 0),

      // BUG: Diagnostic contains:
      this.toString() + s,
      super.toString() + s,
      // BUG: Diagnostic contains:
      i.toString() + s,
      i.toString(16) + s,
      // BUG: Diagnostic contains:
      String.valueOf(i) + s,
      // BUG: Diagnostic contains:
      String.valueOf(0) + s,
      // BUG: Diagnostic contains:
      String.valueOf((String) null) + s,
      String.valueOf(null) + s,
      String.valueOf(new char[0]) + s,
      String.valueOf(new char[0], 0, 0) + s,
      //
      this.toString() + 42,
      super.toString() + 42,
      i.toString() + 42,
      i.toString(16) + 42,
      String.valueOf(i) + 42,
      String.valueOf(0) + 42,
      // BUG: Diagnostic contains:
      String.valueOf((String) null) + 42,
      String.valueOf(null) + 42,
      String.valueOf(new char[0]) + 42,
      String.valueOf(new char[0], 0, 0) + 42,

      // BUG: Diagnostic contains:
      this.toString() + this.toString(),
      super.toString() + super.toString(),
      // BUG: Diagnostic contains:
      i.toString() + i.toString(),
      i.toString(16) + i.toString(16),
      // BUG: Diagnostic contains:
      String.valueOf(i) + String.valueOf(i),
      // BUG: Diagnostic contains:
      String.valueOf(0) + String.valueOf(0),
      // BUG: Diagnostic contains:
      String.valueOf((String) null) + String.valueOf((String) null),
      String.valueOf(null) + String.valueOf(null),
      String.valueOf(new char[0]) + String.valueOf(new char[0]),
      String.valueOf(new char[0], 0, 0) + String.valueOf(new char[0], 0, 0),
    };
  }

  int[] m2() {
    return new int[] {
      1 + 1, 1 - 1, 1 * 1, 1 / 1,
    };
  }
}

import java.math.BigInteger;

class A {
  private final BigInteger i = BigInteger.ZERO;
  private final String s = i.toString();

  void m() {
    StringBuilder sb = new StringBuilder();

    sb.append(1);
    sb.append(i);
    // BUG: Diagnostic contains:
    sb.append(i.toString());
    sb.append(i.toString(16));
    // BUG: Diagnostic contains:
    sb.append(String.valueOf(i));
    // BUG: Diagnostic contains:
    sb.append(String.valueOf(0));
    // BUG: Diagnostic contains:
    sb.append(String.valueOf((String) null));
    sb.append(String.valueOf(null));
    sb.append(String.valueOf(new char[0]));
    sb.append(String.valueOf(new char[0], 0, 0));
    sb.append(s);
    sb.append("constant");

    sb.insert(0, 1);
    sb.insert(0, i);
    // BUG: Diagnostic contains:
    sb.insert(0, i.toString());
    sb.insert(0, i.toString(16));
    // BUG: Diagnostic contains:
    sb.insert(0, String.valueOf(i));
    // BUG: Diagnostic contains:
    sb.insert(0, String.valueOf(0));
    // BUG: Diagnostic contains:
    sb.insert(0, String.valueOf((String) null));
    sb.insert(0, String.valueOf(null));
    sb.insert(0, String.valueOf(new char[0]));
    sb.insert(0, String.valueOf(new char[0], 0, 0));
    sb.insert(0, s);
    sb.insert(0, "constant");

    sb.replace(0, 1, i.toString());
  }
}

import java.util.Formattable;
import java.util.Locale;

class A {
  private final Locale locale = Locale.ROOT;
  private final Formattable f = (formatter, flags, width, precision) -> {};
  private final Object o = new Object();
  private final String s = o.toString();

  void m() {
    String.format(s, f);
    String.format(s, o);
    String.format(s, s);
    String.format(s, f.toString());
    // BUG: Diagnostic contains:
    String.format(s, o.toString());
    // BUG: Diagnostic contains:
    String.format(s, String.valueOf(o));

    String.format(locale, s, f);
    String.format(locale, s, o);
    String.format(locale, s, s);
    String.format(locale, s, f.toString());
    // BUG: Diagnostic contains:
    String.format(locale, s, o.toString());
    // BUG: Diagnostic contains:
    String.format(locale, s, String.valueOf(o));

    String.format(o.toString(), o);
    // BUG: Diagnostic contains:
    String.format(s.toString(), o);
    String.format(locale.toString(), s, o);
    String.format(locale, o.toString(), o);
    // BUG: Diagnostic contains:
    String.format(locale, s.toString(), o);
  }
}

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.base.Verify.verify;
import static com.google.common.base.Verify.verifyNotNull;

import java.util.Formattable;

class A {
  private final Formattable f = (formatter, flags, width, precision) -> {};
  private final Object o = new Object();
  private final String s = o.toString();

  void m() {
    checkState(true, s, f);
    // BUG: Diagnostic contains:
    checkState(true, s, f.toString());
    checkState(true, f.toString(), f);
    // BUG: Diagnostic contains:
    checkState(true, s.toString(), f);

    checkArgument(true, s, f);
    // BUG: Diagnostic contains:
    checkArgument(true, s, f.toString());
    checkArgument(true, f.toString(), f);
    // BUG: Diagnostic contains:
    checkArgument(true, s.toString(), f);

    checkNotNull(o, s, f);
    // BUG: Diagnostic contains:
    checkNotNull(o, s, f.toString());
    checkNotNull(o, f.toString(), f);
    // BUG: Diagnostic contains:
    checkNotNull(o, s.toString(), f);
    checkNotNull(o.toString(), s, f);

    verify(true, s, f);
    // BUG: Diagnostic contains:
    verify(true, s, f.toString());
    verify(true, f.toString(), f);
    // BUG: Diagnostic contains:
    verify(true, s.toString(), f);

    verifyNotNull(o, s, f);
    // BUG: Diagnostic contains:
    verifyNotNull(o, s, f.toString());
    verifyNotNull(o, f.toString(), f);
    // BUG: Diagnostic contains:
    verifyNotNull(o, s.toString(), f);
    verifyNotNull(o.toString(), s, f);
  }
}

import java.util.Formattable;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.Marker;
import org.slf4j.MarkerFactory;

class A {
  private static final Logger LOG = LoggerFactory.getLogger(A.class);

  private final Marker marker = MarkerFactory.getMarker(A.class.getName());
  private final Formattable f = (formatter, flags, width, precision) -> {};
  private final Object o = new Object();
  private final String s = f.toString();
  private final Throwable t = new Throwable();

  void m() {
    LOG.trace(s, f);
    // BUG: Diagnostic contains:
    LOG.debug(s, f.toString());
    LOG.info(s, t.toString());
    LOG.warn(s, o, t.toString());
    // BUG: Diagnostic contains:
    LOG.error(s, o.toString(), t.toString());
    // BUG: Diagnostic contains:
    LOG.trace(s, t.toString(), o);

    LOG.trace(marker, s, f);
    // BUG: Diagnostic contains:
    LOG.debug(marker, s, f.toString());
    LOG.info(marker, s, t.toString());
    LOG.warn(marker, s, o, t.toString());
    // BUG: Diagnostic contains:
    LOG.error(marker, s, o.toString(), t.toString());
    // BUG: Diagnostic contains:
    LOG.trace(marker, s, t.toString(), o);

    LOG.trace(f.toString(), f);
    // BUG: Diagnostic contains:
    LOG.debug(s.toString(), f);
    LOG.info(t.toString(), f);
    LOG.warn(marker.toString(), s, f);
    LOG.error(marker, o.toString(), f);
    // BUG: Diagnostic contains:
    LOG.trace(marker, s.toString(), f);
    LOG.debug(marker, t.toString(), f);
  }
}

import java.math.RoundingMode;
import java.util.Objects;

class A {
  static class B {
    String name() {
      return toString();
    }

    static String toString(int i) {
      return Integer.toString(i);
    }

    static String toString(int i, int j) {
      return Integer.toString(i * j);
    }
  }

  enum E {
    ELEM;

    public String toString() {
      return "__" + name() + "__";
    }
  }

  private final B b = new B();
  private final String s = b.toString();

  String[] builtin() {
    return new String[] {
      // BUG: Diagnostic contains:
      s + b.toString(),
      // BUG: Diagnostic contains:
      s + Objects.toString(b),
      // BUG: Diagnostic contains:
      s + String.valueOf(b),
      // BUG: Diagnostic contains:
      s + Boolean.toString(false),
      // BUG: Diagnostic contains:
      s + Byte.toString((byte) 0),
      // BUG: Diagnostic contains:
      s + Character.toString((char) 0),
      // BUG: Diagnostic contains:
      s + Short.toString((short) 0),
      // BUG: Diagnostic contains:
      s + Integer.toString(0),
      s + Integer.toString(0, 16),
      // BUG: Diagnostic contains:
      s + Long.toString(0),
      s + Long.toString(0, 16),
      // BUG: Diagnostic contains:
      s + Float.toString((float) 0.0),
      // BUG: Diagnostic contains:
      s + Double.toString(0.0),
    };
  }

  String[] custom() {
    return new String[] {
      s + b.name(),
      // BUG: Diagnostic contains:
      s + RoundingMode.UP.name(),
      // BUG: Diagnostic contains:
      s + mode().name(),
      s + A.name(),
      s + A.toString(42),
      // BUG: Diagnostic contains:
      s + B.toString(42),
      s + B.toString(42, 42),
    };
  }

  static String name() {
    return A.class.toString();
  }

  RoundingMode mode() {
    return RoundingMode.UP;
  }

  static String toString(int i) {
    return Integer.toString(i);
  }
}