Guava Objects、MoreObjects、ComparisonChain

IDEA can generate straightforward toString, hashCode and equals method, but sometimes is not enough.

Commonclipse, generating plug hashcode, equals method.

Guava on toStirng, hashCode, equals methods are supported, making it easier to customize.

Objects

Objects in the Guava can be customized class equals, hashCode method.

package com.google.common.base;
@GwtCompatible
public final class Objects extends ExtraObjectsMethodsForWeb {
    private Objects() {}

    public static boolean equal(@Nullable Object a, @Nullable Object b) {
    	return a == b || (a != null && a.equals(b));
    }

    public static int hashCode(@Nullable Object... objects) {
    	return Arrays.hashCode(objects);
    }
}

class Demo {
    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }
        Demo demo = (demo) o;

        return Objects.equal(this.name, guava.name)
                && Objects.equal(this.age, guava.age)
                && Objects.equal(this.birthday, guava.birthday);
    }
    
    @Override
    public int hashCode() {
    	// Guava Objects hashCode 底层调用了 Arrays.hashCode
        return Objects.hashCode(name,age,birthday);
    }
}

MoreObjects

Guava in MoreObjecs toString method provides customized support.

@GwtCompatible
public final class MoreObjects {

	// 返回两个给定参数第一个不为空的参数，如果都是空，抛出NullPointerException
    public static <T> T firstNonNull(@Nullable T first, @Nullable T second) {
        return first != null ? first : checkNotNull(second);
    }

	// 返回ToStringHelper对象(内部类)
    public static ToStringHelper toStringHelper(Object self) {
    	return new ToStringHelper(self.getClass().getSimpleName());
    }
    public static ToStringHelper toStringHelper(Class<?> clazz) {
    	return new ToStringHelper(clazz.getSimpleName());
    }
    public static ToStringHelper toStringHelper(String className) {
    	return new ToStringHelper(className);
    }

 
  	public static final class ToStringHelper {
        private final String className;
        private final ValueHolder holderHead = new ValueHolder();
        private ValueHolder holderTail = holderHead;
        private boolean omitNullValues = false;

        private ToStringHelper(String className) {
            this.className = checkNotNull(className);
        }

  		// 省略值为null的字段
        @CanIgnoreReturnValue
        public ToStringHelper omitNullValues() {
            omitNullValues = true;
            return this;
        }
		
		// 添加属性以及对应的值
        @CanIgnoreReturnValue
        public ToStringHelper add(String name, @Nullable Object value) {
          	return addHolder(name, value);
        }


  
        @CanIgnoreReturnValue
        public ToStringHelper addValue(@Nullable Object value) {
          	return addHolder(value);
        }
      

        @Override
        public String toString() {
            // create a copy to keep it consistent in case value changes
            boolean omitNullValuesSnapshot = omitNullValues;
            String nextSeparator = "";
            StringBuilder builder = new StringBuilder(32).append(className).append('{');
            for (ValueHolder valueHolder = holderHead.next;
                valueHolder != null;
                 valueHolder = valueHolder.next) {
                    Object value = valueHolder.value;
                	if (!omitNullValuesSnapshot || value != null) {
                  		builder.append(nextSeparator);
                  		nextSeparator = ", ";

                        if (valueHolder.name != null) {
                            builder.append(valueHolder.name).append('=');
                        }
                        if (value != null && value.getClass().isArray()) {
                            Object[] objectArray = {value};
                            String arrayString = Arrays.deepToString(objectArray);
                            builder.append(arrayString, 1, arrayString.length() - 1);
                    } else {
                    	builder.append(value);
                    }
                }
            }
          	return builder.append('}').toString();
       }    
		    
	   // 添加节点
       private ValueHolder addHolder() {
           ValueHolder valueHolder = new ValueHolder();
           holderTail = holderTail.next = valueHolder;
           return valueHolder;
       }
       private ToStringHelper addHolder(@Nullable Object value) {
           ValueHolder valueHolder = addHolder();
           valueHolder.value = value;
           return this;
       }
       private ToStringHelper addHolder(String name, @Nullable Object value) {
           ValueHolder valueHolder = addHolder();
           valueHolder.value = value;
           valueHolder.name = checkNotNull(name);
           return this;
       }

	   // 属性名-属性值 节点对象，像链表一样串在一起
       private static final class ValueHolder {
           String name;
           Object value;
           ValueHolder next;
       }
    }

  	private MoreObjects() {}
}





class Deom {
    @Override
    public String toString() {
        return MoreObjects.toStringHelper(this)
                .omitNullValues()					 // 省略空
                .add("name", this.name)				 // 添加属性名、属性值
                .add("age", this.age)
                .add("birthday", this.birthday)
                .toString();						 // MoreObjects核心方法
    }
}

ComparisonChain

Guava ComparisonChain is provided a comparator, that can be simplified if-else large numbers of code manually ten days compareTo method, the comparator becomes elegant.

class Demo {
    @Override
    public int compareTo(Guava o) {
        return ComparisonChain.start()
                .compare(this.name, o.name)
                .compare(this.age, o.age)
                .compare(this.birthday, o.birthday)
                .result();
    }
}

ComparisonChain is an abstract class, there are three main internal method.

public abstract class ComparisonChain {
	// 构造私有，只提供静态方法
	private ComparisonChain() {}
  
  	// 返回ComparisonChain的一个内部类对象，该内部类中进行了抽象方法的实现
  	public static ComparisonChain start() {
    	return ACTIVE;
    }
    
    // 大量比较方法的重载，由内部类进行了实现
    public abstract ComparisonChain compare(Comparable<?> left, Comparable<?> right)
    
    // 返回了比较的结果，在内部类中进行了实现
    public abstract int result();
}